This invention relates to a casting cutting device for continuous casting machines. More particularly, it relates to a device for cutting a casting that is continuously withdrawn from a continuous casting machine, while maintaining the temperature of the casting.
As shown in FIG. 1, a continuous caster generally casts molten steel 2 stored in a tundish 1 into a mold 3 where the steel is formed into a casting 4 of the desired shape. The casting 4 is continuously withdrawn through withdrawal guide rollers (hereinafter called guide rollers) 5 onto a horizontal conveyor table 6 following the guide rollers 5. A cutting device 7 mounted on the conveyor table 6 cuts the casting 4 into desired lengths.
The cutting device 7 is movable along and above the conveyor table 6 synchronously with the traveling speed of the casting 4, so that the cutting device 7 can cut the casting 4 continuously supplied onto the conveyor table 6 without interrupting the operation of the continuous caster.
FIGS. 2 and 3 are a side elevation and a cross section of the conveyor table 6 and cutting device 7 of the conventional ordinary design. As illustrated, the conveyor table 6 comprises a forward conveyor table 6a, a rearward conveyor table 6c (the terms "forward" and "rearward" used herein designate relative positions in relation to the traveling direction of the casting 4), and a lifting roller table 6b. The cutting device 7 comprises a frame 71 straddling the conveyor table 6, runners 72 which movably support the frame 71 while running on rails 8 laid along and on either side of the conveyor table 6, a clamp mechanism 73 carried by the frame 71 so as to be movable across the width of the casting 4, and a flame cutting torch 74.
As shown in FIG. 3, the clamp mechanism 73 comprises a threaded bar 731 rotatably supported by and transversely extending along the frame 71 and a pair of clamp cars 732 engaged with the threaded bar 731. The threaded bar 731 is rotated by a motor 734 equipped with a reduction gear, whereby the clamp cars 732 move transversely. A transversely swingable clamp arm 735 is fitted to the bottom of each clamp car 732, and the rod of a swinging air cylinder 736 is connected to the clamp arm 735. The motor 734 rotates the threaded bar 731 to bring the clamp cars 732 close to both sides of the casting 4. Then, the air cylinders 736 are actuated to clamp the casting 4 with the clamp arms 735.
The flame cutting torch 74 is fastened to a transversely movable saddle 741 mounted on the frame 71, following the clamp mechanism 73. Engaged with a threaded bar 743 rotated by a motor 742 equipped with a reduction gear, the saddle 741 moves transversely during the rotation of the threaded bar 743. The saddle 741 moves at a constant speed so that the torch 74 advances from one side to the other to cut the casting 4 widthwise.
To cut the casting 4 with the cutting device 7, the clamp mechanism 73 clamps both sides of the casting 4 when the cutting point, which is spaced from the head end of the casting 4 by a desired length, passes below the cutting device 7 standing ready for operation in the starting position as shown in FIG. 2. The desired length is determined by a measuring device such as a measuring roll. When the clamping is accomplished, the cutting device 7 is synchronously moved forward by the casting 4, through the frame 71 and runner 72. At the same time, the torch 74 starts to cut the casting 4, using a hot flame. As the casting 4 travels forward, the torch 74 moves sideward to cut across the casting 4. On completion of the cut, the clamp mechanism 73 is released to stop the forward movement of the frame 71, and a drive motor 75 returns the cutting device 7 to its starting position, ready for the next cutting operation. Because the torch 74 is traversed at a constant speed, completion of the cut can be accomplished in the time elapsed since the start of the cut. Such operations as the stopping of the cutting, the release of the clamp mechanism, and the withdrawal of the cutting device 7 are automatically controlled by a sequence circuit (not shown) including a timer.
The cutting device 7 moves mainly over the lifting roller table 6b. When the casting 4 being flame-cut passes over the lifting roller table 6b from conveyor rollers 60c on table 6c to conveyor rollers 60a on table 6a, lifting conveyor rollers 60b provided thereon are lowered by an up-down mechanism 9, whereby the conveyor rollers 60b are protected from the chips from the cutting operation and the cutting flame.
The conventional practice has been that the casting 4, cut to the desired length by the cutting device 7, is cooled on cooling beds etc., cold-scarfed or stockpiled, then reheated in a heating furnace and delivered to the subsequent rolling-mill line. Solidification of the casting 4 has been completed by the time the casting 4 moves onto the conveyor table 6, clearing the guide rollers 5. On completion of the solidification, the casting 4 still has a high temperature of 1,000.degree. C. or above. Accordingly, the conventional practice has called for costly installation and maintenance of the cooling equipment and heating furnace and, also, has involved considerable energy losses. To eliminate these shortcomings, several attempts have been made at so-called hot charging, which varies from delivering the as cut uncooled casting 4 direct into the rolling process to heating the casting 4 in a heating furnace to a temperature suited for the subsequent rolling operation. Because of the extensive temperature drop during the passage through the guide rollers 5 and over the conveyor table 6, however, the casting 4 has seldom maintained a sufficiently high temperature to permit direct rolling, entailing considerable heating in the heating furnace. Especially, cutting the casting 4 with a traversing torch takes a long time (e.g. 2 to 5 minutes), during which the casting temperature drops by 100.degree. C. or more.
Some temperature-conserving devices have been proposed to prevent the temperature drop in the casting, too. In the vicinity of the conveyor table 6, however, the cutting device 7 moves back and forth frequently, as described previously. A dummy bar, which is inserted before the start of a cast, is removed. Scale and other foreign matter (hereinafter collectively called the scale) dropping from the traveling casting 4 are removed in this area, too. In addition, many conveyor rollers 60, a drive mechanism 601 therefor, and other equipment are provided in a limited space thereabout. Because of these difficulties, no simple, compact and effective temperature-maintaining equipment has been developed which as a practical matter can be installed in the limited space and surely prevent the temperature drop in the casting 4.